Big Spring VS Coilovers

[Racer Roy]

Hello there, happy new year:
I have a question for your wisdom.
I am going touring with my big spring offset late model this year and I am looking for some setup info so I can have a decent baseline.
I am borrowing some notes from a friend who has raced the tracks we will be going to, but his cars are all coilovers.
I know this is a dirt forum and we are on pavement, but the formula I am looking for should be the same regardless of surface.
I have raced on a 1/4 mile flat track with the following (big springs on Camaro lowers):
750RF 800LF 175RR 200LR
He ran the same track on coilovers with:
250RF 275LF 175RR 200LR

On the high bank 3/8 oval, he went up to 325 on both front springs with success.

What rates would you suggest I start at for my big spring front to be close to what his car was with 325's?
Is there a publication that has these formulas, possibly from the beginning of the coilover era?
Also, to avoid the BBSS/bumpstop debate, I know these numbers are all old school, but that is what I have to work with for this season. My car is very competitive on the flat tracks and I am hoping to be decent on the big tracks.
Thanks for the opinions, cheers

RR

[Racer Roy]

I have been doing research and I need to determine the "wheel rates" of both cars and see where that takes me.
I still have not found a good chassis setup book for this and other tips. Any suggestions? Are the Steve Smith books still a good source?

RR

[dynoman14]

Motion ratio on most stock front ends is about 2:1. We used to double the rates of coil-over cars when we ran big springs on the front. That is a rough estimate to get you close. If you are running high pressure gas shocks you might want to consult your shock builder as he will have a better idea of what you might need.

[clm15]

I am from the dirt,but 275 and 250 seem light for a car with grip and I bet 2600lb.I bet he runs a sway bar! Spring Rate vs Wheel Rate found this so you can do the math, its ez.

--------------------------------------------------------------------------------http://www.miracerros.com/mustang/t_wheel_rate.htm

Spring rate is the amount of force it takes to compress a spring 1-inch. Wheel rate is the spring rate actually measured at the wheel. Both are expressed in lb/in.



In order to calculate wheel rate, you need to know the spring rate, the motion ratio and the spring angle. Then you can solve the following equation.


Wheel Rate = ( ( MotionRatio^2) * SpringRate ) * sine(Spring Angle)

[Racer Roy]

We do use swaybars on the front, ranging from 7/8" to 1 3/16"
I'm using an 1 1/8th for the 1/4 mile. Most use the same on the bigger track, so I was not going to make a change until I run and plan from there.
Of course, those BBSS crazies are using 100lb springs and 2 7/8 bars, all of which is far beyond my modest car.
As I talk to people, I am finding that the ultra soft bumpstop setups are hard to dial in on a flat track. It's the high bank tracks where I need the most help.
The next thing I need to learn about is shocks. I'll start a new thread for that.

Thanks for the links.

RR

[balljoint]

Roy I run a bigspring too on pavement too. A newer Port City Elite.

Always learning. PM me.

[Racer Roy]

Hey there, Balljoint: Port city's are pretty popular here. I sent you a PM

RR